Part of the weight of the world was lifted from the shoulders of scientists recently.

Physicists at the University of Washington in Seattle have re-calculated the mass of the Earth using a new measurement of the force of gravity and determined that the planet is lighter than previously thought.

"That is a huge embarrassment..." said Jens Gundlach, a research associate physics professor. "We think we know everything so well and other constants are defined to many, many digits."

The new estimate puts the Earth's mass at 5,972 billion billion tonnes, down from the previous estimate of 5,978 billion billion tonnes.

We are confident that we know the mass of our home planet Earth now more precisely than it has ever been known to mankind," said Mr Gundlach, who presented his findings to the American physical society in Long Beach, California, with his colleague, researcher Stephen Merkowitz.

The new measurement comes from a re-calculation of the force of gravity, a constant represented by the letter G, which is supposed to be one of three fundamental numbers consistent across the universe. But even though it is more than 300 years since Isaac Newton explained the force universal gravitational attraction, Scientists are still trying to decide how strong it is.

"Gravity is the most pervasive of the fundamental forces." said Barry Taylor, manager of the fundamental constants data centre at the national institute of the standards of technology. The Seattle team, which warned that its findings are preliminary, arrived at the new constant by refining an experiment developed in 1797-98 by Henry Cavendish.

A device called a torsion balance recorded the effects of the gravity of four stainless steel balls on a gold-plated plate. If accepted, the new value would reduce the uncertainty of G by a factor of about 100.